Apparatus for determining the number of microorganisms in the air and a method of operating said apparatus

ABSTRACT

The invention concerns an apparatus which has holder stations (41, 42) for individual parts (3, 5) of a microorganism settlement device (1). This settlement device (1) comprises a lower part (30 with a nutrient medium (4) and a lid (5). The lower part (3) is located in the first holder station (41). The apparatus further has an actuating arrangement (10) designed such that the lid (5) can be moved in controlled manner between the two holder stations (41, 42).

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to an apparatus for determining the numberof microorganisms in air, with a device for the settlement ofmicroorganisms, said device having a lower part and a cover, a nutrientor culture medium being located in the interior of the settlement deviceand to a method for operating this apparatus.

2. Prior Art

To detect the number of microorganisms, in particular germs, such asfungae, bacteria, etc., in air, it is known to cause germs suspended inthe air to settle on a culture medium during a predetermined timespan.This culture medium is then covered and exposed to conditions which areconducive to the reproduction of the settled germs. After apredetermined timespan has elapsed, seats or zones on the culture mediumwhich result from the growth of the settled germs are counted.

A so-called Petri dish, which has a lower part with a nutrient medium aswell as a cover, is used for carrying out this method. The cover isremoved from the lower part and the Petri dish is left open during adesired timespan. The Petri dish is then closed again by hand. Theaccuracy of this way of measuring the number of germs in air dependslargely on the carefulness of the person who carries out thesemeasurements manually. Moreover, this previously known method makes itnecessary for the person carrying out such measurements to be presentduring the entire measuring operation. This is unfavorable, inparticular, when such measurements have to be carried out outside theusual work time, in a place where access is difficult, etc.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is to eliminate said and furtherdisadvantages of the prior art.

Embodiments of the present invention are explained in more detail belowwith reference to the accompanying drawings in which:

FIG. 1 shows a side view of a first version of the present apparatus,

FIG. 2 shows a top view of the apparatus from FIG. 1,

FIG. 3 shows a side view of a second version of the present apparatus,

FIG. 4 shows a top view of the apparatus from FIG. 3,

FIG. 5 shows the mechanical part of the present apparatus partially in avertical section,

FIG. 6 shows a top view of the lower portion of the mechanical part fromFIG. 5,

FIG. 7 shows a block diagram of the electrical part of the presentapparatus,

FIG. 8 shows a correlation table, and

FIGS. 9 to 14 show a second actuating arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a side view of a first version of the present apparatus,whilst FIG. 2 shows a top view of the apparatus from FIG. 1. Thisapparatus serves for determining the number of germs in air, and itcomprises a device 1 for the settlement of germs and an arrangement 10for actuating this settlement device 1.

The settlement device 1 is designed, in the present case, as a Petridish known per se. The Petri dish 1 has a lower part 3 (FIG. 5) and acover 5. The top side of the floor of the dish lower part 3 is coveredwith a culture or nutrient medium 4, on which microorganisms can settlewhen the Petri dish is open. The settled microorganisms can thenreproduce on the nutrient medium 4 when the Petri dish 1 is closed. Theculture medium 4 advantageously lies in a horizontal plane.

The settlement device 1 is designed, furthermore, in such a way thatgerms or particles can no longer pass into this device 1 during theincubation time. For this purpose, the cover 5 of the Petri dish 1 isdesigned in such a way that its edge part 6 hanging down also preventsgerms from passing onto the lower part 3 during the incubation time. Inthis case, the cover 5 can rest on the upper edge of the dish lower part3 either sealingly or so as to leave a gap between the cover 5 and thelower part 3. In order to form this gap, the underside of the dish cover5 is provided with projections in a way known per se.

The actuating arrangement 10 comprises a housing 11 which has ahorizontally extending upper wall 12, a display or indicator wall 13, abottom 14, a rear wall 15 and side walls 16 and 17. The indicator wall13 runs obliquely rearward from the housing bottom 14, so that thelength or depth of the horizontally extending upper wall 12 is smallerthan the length or depth of the bottom 14. Indicator elements andactuating means (not illustrated) of the present apparatus are mountedon the indicator wall 13.

The actuating arrangement 10 comprises, furthermore, a device 20 forhandling the cover 5 of the settlement device 1. The handling device 20is designed in such a way that the culture medium 4 can remain openduring a desired timespan for the reception of microorganisms. This isachieved, inter alia, in that the cover 5 is moved by the handlingdevice 20 in such a way that the cover 5 can be moved away from thelower part 3 and back to it again.

The handling device 20 has a shaft 21 which runs virtually verticallyand which passes through the upper wall 12 of the housing 11. In thiscase, this shaft 21 is mounted in a bearing 22 which is inserted in theupper wall 12 of the housing 11. This mounting is designed in such a waythat the shaft 21 can not only rotate in the bearing 22, but also bedisplaced and down in its axial direction. Carrying means 25 for thecover 5 of the Petri dish 1 are articulated on the end part of the shaft21, said end part being the upper or being located above the upper wall12 of the housing 11. The displaceability of the shaft 21 in its axialdirection is indicated in FIGS. 1 and 3 by two positions of the carryingmeans 25, said positions being located one above the other.

The carrying means 25 comprise an arm 26 which is articulated at one endon the upper end of the shaft 21 by means of a pin 27. The arm 26 ispivotable relative to the shaft 21 about this pin 27. The stops on theshaft 21, which limit the rotating movement of this arm 26, are designedin such a way that the arm 26 can rotate between its virtuallyhorizontal and its virtually vertical position. The rotating arm 26 hasa quadrangular cross-section, two of the sides 28 and 29 of the latterextending vertically. FIG. 2 illustrates the arm 26 in its retractedposition. When the arm 26 is in this position, the lower part 3 of thePetri dish 1 is free and germs or the like can settle on the culturemedium 4. The first of said side faces 28 of the arm 26 is the frontside of the arm 26. A curved line L shows the path of a point located atthe free end of the arm 26, while this apparatus is in operation.

A carrier 30 for the cover 5 of the Petri dish 1 is fastened to theunderside of the free end part of the pivoting lever 26. This carrier 30has a horizontally extending baseplate 31 which has a virtuallysemicircular contour (FIG. 2). The rectilinearly extending edge 32 ofthe baseplate 31 is engaged to the front side 28 of the pivoting arm 26,in such a way that this edge 32 runs parallel to the front side 28 ofthe arm 26. Consequently, the virtually semicircular portion 33 of thebaseplate 31 projects from the rear side 29 of the pivoting arm 26. Anessentially vertically extending and also semicircularly extending sidewall 35 of this carrier 30 projects downward from the semicircular edge34 of the baseplate 31. The lower edge of this side wall 35 hasadjoining it a gripping wall 36 which has the shape of a portion of aflat and narrow ring. The outer edge of this gripping wall 36 adjoinsthe lower edge of said side wall 35. The inner edge 37 of this grippingwall 36 is free. The baseplate 31, side wall 35 and gripping wall 36 areexpediently in one piece.

The radius of the inner edge 37 on the gripping ring 36 corresponds tothe radius of the lower part 3 of the Petri dish 1. By contrast, theradius of the side wall 35 of the carrier 30 corresponds to the largestradius of the cover 5 of the Petri dish 1, that is to say to the radiusof the lower edge 7 of the hanging-down side wall 6 of the cover 5. Theheight of the side wall 35 of the carrier 30 corresponds to the heightof said side wall 6 of the cover 5. The expression "corresponds" means,here, that said dimensions of the carrier 30 are at least as large asthe corresponding dimensions of the Petri dish 1. The dimensions on thecarrier 30 may be somewhat larger than the corresponding dimensions ofthe Petri dish 1, so that the present apparatus can operate without anyfriction. In fact, the carrier 30 must be dimensioned in such a way thatit can receive and transport the cover 5 without any difficulty. Forthis purpose, the depth, or dimension perpendicular to the arm 26, ofthe essentially semicircular baseplate 31 may be somewhat larger thanthe radius of the lower edge 7 on the cover 5 of the Petri dish 1. Thisadditional depth of the baseplate 31 may correspond, for example, to thewidth of the arm 26, that is to say to the distance between the frontwall 28 and the rear wall 29 of the arm 26. The radius of the inner edge37 of the gripping wall and the width of this gripping wall 36 must besuch that this wall 36 reliably engages under the lower edge 7 of thecover 5 of the Petri dish 1 and holds said edge reliably during thepivoting movement of the carrier 30.

The shaft 21 is arranged approximately in the middle of the length ofthe upper wall 12 of the apparatus housing 11. Reception stations 41 and42 for the individual parts 3 and 5 of the Petri dish 1 are designed onthe top side of the upper wall 12 on the left and right of the shaft 21.The lower part 3 of the Petri dish 1 is accommodated in the firstreception station 41 and is held on the spot by means of position pins43. This first reception station 41 comprises, furthermore, anelectrothermal device 44 (FIGS. 3 and 4) which is advantageously locatedbelow the upper wall 12. By means of this electrothermal device 44, thelower part 3 of the Petri dish 1, together with the culture medium 4 andthe germs settled on the latter, can, depending on the situation, eitherbe heated (incubated), if the ambient temperature is low, or be cooled,if the ambient temperature is too high. This device 44 may contain aso-called Peltier element known per se.

FIG. 2 illustrates the carrier 30, together with the cover 5, in thesecond reception station 42, so that the cover 5 is in its positionremoved from the lower part 3. When the cover 5 is in this position,germs can settle on the culture medium 4 in the lower part 3. In FIG. 4,the cover 5 is illustrated placed on the lower part 3 in the region ofthe first reception station 41, so that further germs can no longerreach the culture medium 4. The carrier 30 is illustrated in itsretracted position in the region of the second reception station 42, sothat the cover 5 is free. FIG. 4 shows only a portion of the cover 5, sothat it is possible to look into the interior of the Petri dish 1 havingthe culture medium 4. A colony 45 is indicated on that portion of theculture medium 4 which is shown in FIG. 4. This colony arose from a germwhich reached the culture medium while the lower part 3 was uncovered.

Inside the housing 11 and below the upper wall 12 of the housing 11 isarranged an auxiliary plate 50 which is fastened to the underside of theupper wall 12 of the housing 11 by means of spacer pieces 51. Thisauxiliary plate 50 runs virtually parallel to the upper wall 12 andcarries, inter alia, a second bearing 52 for the lower end part of theshaft 21. This second bearing 52 is aligned axially with the firstbearing 22. The lower end part of the shaft 21 is designed to be so longthat it projects out of the second or lower bearing 52.

A control disk 55, the circumferential part of which is provided withteeth 56, is mounted rotatably on the top side of the auxiliary plate50. This circumferential part of the control disk 55 is assigned a drivemotor 57, the pinion 58 of which meshes with the teeth 56 on the controldisk 55.

At least one bearing block 59, on which a twoarmed angle lever 60 ismounted pivotably, projects from the underside of the auxiliary plate50. The angle between the arms 61 and 62 of this angled lever 60 isabout 90°. The free end of the first arm 61 of the angled lever 60 isarticulated on the lower end of the shaft 21 by means of a pin 68. Thesecond arm 62 of the angled lever 60 passes through a correspondingorifice in the auxiliary plate 50, so that the free end part of thesecond arm 62 of the angled lever 60 is located in the region of thecontrol disk 55, specifically below the latter. The free end of thesecond arm 62 of the angled lever 60 is provided with a roller 63. Thesurface of this roller 63 has the shape of the surface of a sphericalsegment of two bases, in which the equator of the sphere is located inthe middle of the height of this spherical segment.

In that region of the shaft 21 which is located between the two bearings22 and 52, the shaft 21 is provided with a toothed rim 64 whichsurrounds the shaft 21 and which is firmly connected to the shaft 21. Ahorizontally arranged and displaceable rack 65 is provided, which islocated above the control disk 55 and the teeth 66 of which mesh withthe toothed rim 64 on the shaft 21. The underside of the rack 65 carriesa guide roller 67 which projects virtually at right angles from thebasic body of the rack 65.

A control cam 71 and 72 is designed in each case in the upper and thelower large-area side of the control disk 55. In the instanceillustrated, these control cams 71 and 72 are designed as depressions orgrooves in the large-area sides of the basic body of the control disk55, said depressions or grooves having an essentially quadrangular crosssection. The lower control cam 71 serves for controlling the verticalmovement of the carrying means 25 for the cover 5 of the Petri dish 1.The roller 63 of the second arm 62 of the angled lever 60 is located inthis control cam 71. The upper control cam 72 serves for controlling thepivoting movements of the carrier 30 of the carrying means 25 in thehorizontal direction. The guide roller 67 on the rack 65 is located inthis control cam 72.

The first control cam 71 has essentially the shape of a spiral with asingle turn. When the control disk 55 executes a revolution, the roller63 on the second arm 62 of the angled lever 60, said roller beinglocated in this control cam 71, is displaced in the radial direction ofthe control disk 55. In this case, that end of the first arm 61 of thisangled lever 60 which is connected to the shaft 21 moves the shaft 21 inthe vertical direction. The shaft 21 moves either upward or downward,depending on the direction of rotation of the control disk 55. Thesecond control cam 72 is nonround and has portions which allow a to andfro horizontal movement of the carrier 30 of the cover 5 or a standstillof this carrier 30. During these standstill portions, the carrier 30 ismoved in the vertical direction by means of the first control cam 71, asdescribed above.

The measures described make it possible for the carrying means 25 toexecute simultaneously two movements which are necessary in order tomove the cover 5 of the Petri dish between the first station 41 and thesecond station 42. Said measures also make it possible to place thecover 5 in the first station 41 onto the lower part 3 of the Petridish 1. The carrier 30, without the cover 5, is then moved back againalong the curve L into the second station 42 until it assumes theposition which is illustrated in FIG. 2.

A Petri dish 1, in which its cover 5 is placed on its lower part 3, isbrought into the first station 41 of the present apparatus by hand.After one of the operations has been selected, the carrier 30 for thecover 5 of the Petri dish 1 moves along the curve L out of the secondstation 42 into the first station 41, this carrier 30 being located inits lower position. This horizontal movement ends when the front edge 37of the gripping wall 36 on the carrier 30 comes into the vicinity of thelower part 3 of the Petri dish 1 or even touches the side wall of thislower part 3. In this case, the gripping wall 36 of the carrier 30 comesto rest under the lower edge 7 of the side wall 6 of the cover 5. Theshaft 21 is then moved upward, so that the cover 5 is lifted off fromthe lower part 3 due to the gripping wall 36 of the carrier 30 beinglocated under the cover wall 6. The carrier 25, together with the cover5, then moves back into the second station 42, said carrier beinglocated in its upper vertical position.

After a timespan provided for the settling of germs on the culturemedium 4 has elapsed, the carrier 25, together with the cover 5, movestoward the first station 41, said carrier still being in its upperposition. In the first station 41, the carrier 30 is lowered, with theresult that the cover 5 is set down on the lower part 3 of the Petridish 1. In this lower position, the carrier 25 then moves back into thesecond station 42.

After the Petri dish 1 has been closed, germs which have settled on theculture medium 4 during the opening time of the Petri dish 1 can grow toform colonies 45. After a predetermined timespan, the number of saidcolonies is counted, and the number of microorganisms in the air can beinferred from this.

So that these and further work steps can be executed automatically, theapparatus is equipped with a control device 80. This control device 80is accommodated in the housing 11 of the apparatus and contains acontrol unit 81 which comprises a microprocessor 82, a regulating unit83, a timer 84 and an EEPROM 85. This control unit 81 is supplied bymeans of a feed 86 with electrical current which is also used forfeeding the motor 57. The respective operating mode of the apparatus isentered by means of keys 87 which are located, together with indicatormeans 88 known per se, in the region of the indicator wall 13 of theapparatus housing 11. For the automatic control sequence, it isnecessary to provide position sensors 89 for detecting the position ofthe carrier 30. These are arranged at respective points along the path Lof the carrier 30. Furthermore, the control device 80 also comprisestemperature sensors 90 which are mounted in the region of the firststation 41.

The EEPROM 85 stores, inter alia, programs for handling the Petridish 1. These programs may contain various conditions, such as, forexample, time, temperature, etc., for the incubation of the settledmicroorganisms on the culture medium 4. Together with the selection ofsuitable culture media 4, such programs may be used for a selectivecapture of microorganisms.

Since the quantity of microorganisms in the air also depends on theheight above the ground, it is expedient to provide a stand (notillustrated), on which the housing 11 of the apparatus is fastened. Sothat the density of the germs can be measured at different heights, thestand is designed in such a way that its height is adjustable.

FIG. 8 shows a table which indicates, inter alia, how the hygienicsituation in rooms has been evaluated hitherto. The particulars in thefirst column of the table, although being relatively clear, use largenumbers, which is cumbersome in practice. The evaluation (CEE) in thesecond column of the table in FIG. 8 does not cover all classes of airhygiene. The "IMA" columns work with particulars relating to ranges,which is likewise cumbersome. The evaluation interpreted in words in thetwo penultimate columns is inaccurate.

In the present case, the individual classes of room evaluation areassigned numbers from 1 to 5 which are directly related to thequantities of particles per cm² and per hour which are specified in thethird column of the table from FIG. 8.

FIG. 9 shows a further possibility for the design of the presentapparatus, specifically in a front view after the front wall of thisapparatus has been removed. Arranged in the housing 11 of the apparatusis a carrying plate 95, on which a second possible version of thearrangement 100 for actuating the settlement device 1 is mounted. FIG.10 shows a top view of the most important components of this arrangement100.

The arrangement 100 comprises a crank 101 which is mounted rotatably orpivotably on the carrying plate 95. In the case illustrated, this crank101 is essentially bowl-shaped or sleeve-shaped and has a bottom 102(FIGS. 11 to 14), from which a cylindrical side wall 103 extends upward.The axis of rotation of this crank 101 runs vertically in the caseillustrated and coincides with the main axis A of this arrangement 100.

The underside of the crank bottom 101 has adjoining it a hollow shaft 96which is arranged in the middle of the crank bottom 102 and whichcarries the crank 101. This carrying shaft 96 is mounted rotatably orpivotably in a bearing 97. The pivoting shaft 21 passes through theorifice 99 in the carrying shaft 96 us [sic] is mounted both pivotablyand longitudinally displaceably in this orifice 99. The axis of thecarrying shaft 96 likewise coincides with the main axis A of thisarrangement 100. The bearing 97 is embedded in the carrying plate 95, sothat part of the carrying shaft 96 can project from the underside of thebearing 97. This portion of the carrying shaft 96 is provided with adisk 98 which is firmly connected to the crank 101 via the carryingshaft 96. This disk 98 is connected to the drive motor 57 of thisarrangement 100 via a belt 54.

A slot 104 is made in the wall 103 of the crank 101, said slotconstituting a perforation in the crank wall 103. This slot 104 runsobliquely with respect to the axis A. This means that one end 121 of theslot 104 is lower or nearer to the crank bottom 102 than the other end122 of this slot 104. The angular length of the slot 104 is more than180° and is advantageously 210°. The crank slot 104 has an upperlongitudinal edge 128 and a lower longitudinal edge 129 which extendbetween the ends 121 and 122 of the slot 104 and run continuously.

The arrangement 100 comprises, furthermore, a guide plate 105 which isarranged next to the crank 101 and which runs virtually parallel to aplane, in which the main axis A of this arrangement 100 lies. The guideplate 105 is at a distance from the outside of the crank 101. In theinstance illustrated, the basic body 131 of the plate 105 is essentiallyrectangular, the longer sides 124 and 126 of this rectangle 131 runninghorizontally. The shorter sides 123 and 125 of the rectangle 131 runvertically.

The guide plate 105 has a rectilinear long hole 106 which runs virtuallyhorizontally, that is to say parallel to the longer sides 124 and 126 ofthe guide plate 105, and which is virtually at the same height as theupper end part 122 of the slot 104 in the crank 101. The long hole 106is arranged in relation to the pivoting shaft 21 in such a way that thepivoting shaft 21 is located approximately in the middle of the lengthof the long hole. One of the ends of this long hole 106 is located inone of the sides 125 of the basic body 131 of the guide plate 105, sothat the long hole 106 opens here and adjoins this side 125 of the guideplate 106. By contrast, the other end 127 of the long hole 106 is closedby means of a bottom. The long hole 106 comprises, furthermore, a loweredge 116 and an upper edge 117 which run likewise horizontally, that isto say parallel to the longitudinal sides 124 and 126 of the guide plate105.

The plate 105 has, furthermore, a guide edge 107. This edge 107constitutes a portion of that side 125 of the plate 105 in which theopen end of the long hole 106 is located, the guide edge 107 extendingbetween this open end of the long hole 106 and the underside 126 of theguide plate 105. This guide edge 107 thus runs virtually parallel to themain axis A of this arrangement 100.

The arrangement 100 also comprises a stop 111 which, in the instanceillustrated, has an essentially plate-shaped basic body 141. Thisplate-shaped basic body 141 runs parallel to a plane, in which the mainaxis A of the arrangement 100 lies, said basic body being approximatelyat right-angles to the guide plate 105. That edge 118 of the stop plate111 which is located nearest to the guide plate 105 is assigned to theguide edge 107 of the guide plate 105, specifically in such a way that agap is free between these edges 107 and 118. The stop edge 118, althoughrunning parallel to the guide edge 107, is longer than the guide edge107. The upper end of the stop edge 118 is higher than the upper end ofthe guide edge 107, so that a portion of the stop edge 118 is oppositethe open mouth of the long hole 106 in the guide plate 105.

A bolt 120 is fastened at one end to the shaft 21 and projects virtuallyat right-angles from this shaft 21. The bolt 120 is arranged on theshaft 21 in such a way and designed to be so long that it can passthrough the slot 104 in the crank 101 and that its free end part islocated in the region of the guide plate 105. The cross section of thebolt 120 is circular. The width of the slot 104, of the long hole 106and of the already mentioned gap between the guide edge 107 and the stopedge 118 corresponds to the diameter of the bolt 120, specifically insuch a way that the bolt 120 can move in the slot 104, in the long hole120 [sic] and in said gap with as little friction as possible.

In describing the mode of operation of this arrangement 100, we canstart from the situation in which the bolt 120 is located at the bottomin the crank slot 104 and in the gap between the edges 107 and 118. Inthis case, the cover of the Petri dish is placed on the lower part ofthe latter. When the crank 101 is rotated clockwise by means of thedrive 57, the bolt 120 butts on the guide edge 107 and, due to theascent of the crank slot 104, the bolt 120 moves upward along this guideedge 107, until it has reached the height of the open mouth of the longhole 106 in the guide plate 105. During this phase, the pivoting shaft21 coupled to the bolt 120 executes a lifting movement directed upward,and at the same time the cover of the Petri dish is lifted off from thelower part of the latter.

At the end of the lifting movement, the bolt 120 is opposite the openend of the long hole 106 in the guide plate 105. However, since thedrive 57 drives the crank 101 further in the same direction, the bottomof the upper end 122 of the crank slot 104 presses the bolt 120 into theguide long hole 106 and moves said bolt in the long hole 106 until thebolt 120 butts on the long hole bottom 127. During this phase, the shaft21 has executed a pivoting movement and, at the same time, the cover ofthe Petri dish has been removed from the lower part.

When the direction of rotation of the drive 57 is then reversed, thecrank 101 moves counterclockwise. The bolt 120 is pressed against theopen end of the long hole 106 by the upper and obliquely descending edge128 of the crank slot 104 in this long hole 106. The bolt 120 moves inthe long hole 106, until it butts on the stop edge 118 located oppositethis end of the long hole. The shaft 21 has been pivoted back duringthis movement of the bolt 120, so that the cover of the Petri dish hasbeen returned to the lower part of the latter.

The crank 101 is pivoted or rotated further in the same direction by thedrive 57. In this case, the bolt 120 is in abutment on the stop edge118, so that it cannot move any further in the horizontal direction.However, said gap between the edges 107 and 118 is now located under thebolt 120, and the bolt 120 is pressed into this gap by the descendingslot 104. At the same time, the shaft 21 executes a lifting movementdirected downward and the cover of the Petri dish is placed onto thelower part of the latter.

What is claimed is:
 1. Apparatus for determining the number ofmicroorganisms in air, with a settlement device (1) for the settlementof microorganisms, which has a lower part (3) and a cover (5), anutrient medium (4) being located in an interior of the settlementdevice (1), with an arrangement (10) for actuating the cover (5) of thesettlement device (1), with two reception stations (41, 42) for thesettlement device (1), whereby the actuating arrangement (10) isdesigned in such a way that the cover (5) can be moved in a controlledway between the two reception stations (41, 42), and whereby theactuating arrangement (10) comprises a device (20) for handling thecover (5) and a device (80) for controlling the movements of the cover(5), wherein the handling device (20) comprises a shaft (21) which runsvirtually vertically and which is arranged between the two receptionstations (41, 42), wherein carrying means (25) for the cover (5) areengaged to a first end of the shaft (21), and means for the mechanicalmovement of the shaft (21) are engaged to a second end of the shaft(21),wherein the movement means comprise a motor (57) capable of beingcontrolled by the control device (80), the movement means having, acontrol disk (55) which is driven by the motor (57), the control disk(55) having control cams (71, 72) and the movement means having a lever(60) and a rack (65) which are engaged to the control cams (71, 72) onthe control disk (55) and to the shaft (21).
 2. Apparatus according toclaim 1, wherein the shaft (21) is vertically oriented and is surroundedwith a toothed rim (64) in a region of its surface, that the rack (65)is horizontally arranged and displaceable and is equipped with teeth(66) which are form-locked with the toothed rim (64) of the rack (65).3. Apparatus according to claim 2, wherein the control cams (71, 72) aregrooves in the large-area sides of the control disk (55), that each sideof the control (55) carries preferably one control cam and that a firstcam (72) is engaged to the rack (65) and that a second cam (71) isassigned control of the horizontal movement of the carrying means (25)and is assigned control of the vertical movement of the carrying means(25) and is engaged to the lever (60).
 4. Apparatus according to claim3, wherein each the lever (60) and the rack (65) are equipped withroller (63, 65), said rollers (63, 65) being located in the grooves ofthe control cams (71, 72).
 5. Apparatus according to claim 4, whereinthe lever (60) is a two-armed lever comprising two arms (61 and 62) andthat the angle between the arms (61, 62) of this lever (60) is about 90°and wherein the free end of a first arm (61) is articulated on the shaft(21) and wherein the free end of a second arm (62) is provided with theroller (63) for contacting the control cam.
 6. Apparatus according toclaim 4, wherein said roller has a spherical shape.
 7. Apparatusaccording to claim 1, wherein the carrying means (25) comprise an arm(26) which is connected at a first end to the first end of the shaft(21), and in that a carrier (30) for the cover (5) of the dish (1) ismounted on a second end of the arm (26).
 8. Apparatus according to claim1, wherein the control device (80) comprises a microprocessor (82), aregulating unit (83), a timer (84) and an EEPROM (85) which areelectrically connected together as well as means for manual actuation ofthe control device (80), in that sensors (89, 90) are connected toinputs of the control device (80), and in that the motor (57) isconnected to one of the outputs of the control device (80).
 9. Apparatusaccording to claim 1, wherein a thermoelectric device (44) is arrangedin a region of a first reception station (41) of the two receptionstations (41, 42), and in the thermoelectric device (44) may be aPeltler device.
 10. Apparatus according to claim 1, wherein a stand isprovided, on which remaining parts of the apparatus are mounted, and inthat the stand may be designed in such a way that a height of the standis adjustable.
 11. Apparatus according to claim 1, wherein thesettlement device (1) is a Petri dish.
 12. Method for operatingapparatus for determining the number of microorganisms in air, saidapparatus having a settlement device (1) for the settlement ofmicroorganisms, which has a lower part (3) and a cover (5), a nutrientmedium (4) being located in an interior of the settlement device (1),with an arrangement (10) for actuating the cover (5) of the settlementdevice (1), with two reception stations (41, 42) for the settlementdevice (1), whereby the actuating arrangement (10) is designed in such away that the cover (5) can be moved in a controlled way between the tworeception stations (41, 42), and whereby the actuating arrangement (10)comprises a device (20) for handling the cover (5) and a device (80) forcontrolling the movements of the cover (5), wherein the handling device(20) comprises a shaft (21) which runs virtually vertically and which isarranged between the two reception stations (41, 42), wherein carryingmeans (25) for the cover (5) are engaged to a first end of the shaft(21), and means for the mechanical movement of the shaft (21) areengaged to a second end of the shaft (21),wherein the nutrient medium(4) is exposed to air during a predetermined timespan, in such a waythat microorganisms present in the air can settle on the nutrient medium(4), in that the nutrient medium is covered after a predeterminedtimespan has elapsed, in that after an incubation time has elapsed,visible colonies caused by the microorganisms on the nutrient medium arecounted, and a value for an air germ count is obtained from the visiblecolonies, and in that the evaluation of a room investigated is expresson a basis of the air germ count by particles per cm² per hour. 13.Apparatus for determining the number of microorganisms in air, withsettlement device (1) for the settlement of microorganisms, which has alower part (3) and a cover (5), a nutrient medium (4) being located inan interior of the settlement device (1), with an arrangement (100) foractuating the cover (5) of the settlement device (1), whereby theactuating arrangement (100) is designed in such a way that the cover (5)can be moved in a controlled way between the two reception stations (41,42), and whereby the actuating arrangement (100) comprise a device (20)for handling the cover (5) and a device (80) for controlling movementsof the cover (5), wherein the handling device (20) comprises a shaft(21) which runs virtually vertically and which is arranged between thetwo reception stations (41, 42), wherein carrying means (25) for thecover (5) are engaged to a first end of the shaft (21), and means forthe mechanical movement of the shaft (21) are engaged to a second end ofthe shaft (21), wherein the movement means comprise a motor (57) capableof being controlled by the control device (80), the movement meanshaving a control crank (101) which is driven by the motor (57), thecrank (101) having a control slot (104) and the movement means having abolt (120) which is engaged to the slot (104) and to the shaft (21). 14.Apparatus according to claim 13, wherein the crank (101) is essentiallysleeve-shaped, having an inner orifice (99) and a cylindrical side wall(103), and wherein the crank (101) has an axis of rotation that runsessentially vertically and coincides with the longitudinal axis A of thearrangement (100) and the shaft (21), said shaft (21) being mounted bothpivotably and longitudinally displaceable in the orifice (99) of thecrank (101).
 15. Apparatus according to claim 14, wherein the controlslot (104) is executed as a perforation in the cylindrical side wall(103) of the crank and is running obliquely with respect to thelongitudinal axis A of the arrangement (100), wherein the angular lengthof the slot (104) is more than 180°, and wherein the bolt (120) isfastened at one end to the shaft (21) and projects from the shaft (21)in such a way that it can pass through the slot (104) in the crank (101)and is with its free end movably beared on a guide plate or means (105).16. Apparatus according to claim 15, wherein the angular length is morethan 210°.